1. Field of the Invention
The present invention relates to a wireless communication system that performs closed-loop transmit diversity, and more specifically, relates to a mobile station apparatus that receives a closed-loop transmit diversity signal applied to individual communication channels.
2. Description of the Related Art
[Background Art]
Diversity techniques are effective in mobile communication as a technique for reducing the degradation of transmission quality in a fading environment, and one of the diversity techniques is transmit diversity.
In the transmit diversity, a base station apparatus transmits signals from a plurality of antennas, and a mobile station apparatus uses one antenna and a receiving circuit to receive transmitted signals from the base station apparatus.
When the transmit diversity is performed, the base station apparatus has to grasp the status of a downlink transmission line to the mobile station apparatus prior to signal transmission. A technique whereby feedback information from the mobile station apparatus is used to grasp the status of a transmission line is hereinafter referred to as “closed-loop transmit diversity”.
For example, even 3GPP, which is the standard of a W-CDMA (Wide Band-Code Division Multiple Access) communication system, adopts closed-loop transmit diversity. The transmit diversity is performed by two transmission antennas (hereinafter referred to as “first antenna” and “second antenna”) included in the base station apparatus.
The mobile station apparatus transmits to the base station apparatus, feedback information for controlling a phase of a transmission carrier from the second antenna so as to increase received power of signals received from the base station apparatus. A phase offset applied to the transmission carrier from the second antenna is selected from four phases.
[Related Art]
Related art includes JP-A-2005-341277, “RADIO COMMUNICATION TERMINAL DEVICE AND METHOD FOR CORRECTING TRANSMISSION LINE ESTIMATE OF RADIO COMMUNICATION TERMINAL DEVICE” (MITSUBISHI ELECTRIC CORP).
JP-A-2005-341277 discloses that in a wireless communication terminal device, a feedback information generating section generates feedback information from a transmission line estimate value, an antenna weight estimating section estimates an antenna weight of a radio base station, a synchronous state determination section determines the uplink synchronous state of a transmission line from the feedback information and the result of antenna weight estimation, a phase correction amount determining section determines a phase rotation amount as a correction amount of the transmission line estimate value from the feedback information, the result of antenna weight estimation and the uplink synchronous state, and a transmission line estimate correcting section corrects the transmission estimate value in accordance with the phase rotation amount.
In addition, related art further includes JP-A-2002-118534, “Transmitter/Receiver and Method for Estimating Channel” (SONY INT EUROPE GMBH), JP-A-2008-124643, “Mobile Communication Terminal and Determination Method of Control Volume of Its Phase” (NEC CORP), and JP-A-2010-16836, “Wireless Communication System, Base Station Apparatus, Mobile Station Apparatus and Transmission Control Method” (SHARP KK).